Nice suggestion, but not executable in my case. I draw lines and triangles from 1 buffer and WVP matrix is the same for both. I can't change something only for lines or only for triangles. Changes will affect on all primitives.

In addition to trying out suggestions from this, like I said before, you should also try to introduce some sampler state in your shader now.

My shader is the same. I didn't change anything.

Your suggestion about using VertexShaderOutput instead PixelShaderInput not approached because of VFACE semantic. It is usable only like an input parameter to PixelShader. It cannot be defined in VertexShaderOutput struct

That's why I was saying that please change it a bit and use a sampler state with some basic filtering, like LINEAR.

The way I see that area is going white around your lines is most probably because of aliasing. So once aliasing is out of the way a clearer picture should come out.

And my bad that I kept overlooking the VFACE comment of yours. It makes sense now, why to use one kind of input than the other.

With sampler state I have some problems. I have no idea how to implement it. I found some basic information about samplers, filters etc, but I didn't get it... Maybe you have some useful links or code samples?